Computers and related electronic equipment typically have a number of different types of data storage or memory devices. For example, a read only memory (ROM) is a semiconductor memory device in which data is permanently stored. The data stored on ROM cannot be overwritten or otherwise altered by the user. A ROM is also non-volatile, which means that the data is not destroyed when power is lost. A ROM is programmed during its manufacture by making permanent electrical connections in selected memory cells. ROMs are useful wherever unalterable data or instructions are required. A disadvantage of ROMs is that their programming is determined during the design stage and can only be varied by redesigning the chip.
An alternative to a ROM is a programmable read only memory (PROM) which is programmable once after its manufacture. In one type of PROM, each memory cell is provided with an electrical connection in the form of a fusible link. The PROM is programmed by blowing the fusible link in selected cells. To blow the fuse, current is driven through the link. The current heats the link to its melting point and the link is broken. Usually the link breaks in thinner regions where the current density is highest.
Various means have been used in the past to blow electrically blowable fuses. One recently used technique for opening the connection at the fuse employs the electro-migration effect, which has long been identified as a major metal failure mechanism. Electro-migration is the process whereby the ions of a metal conductor move in response to the passage of a high-density current flow though the conductor. Such motion can lead to the formation of voids in the conductor, which can grow to a size where the conductor is unable to pass current. One can take advantage of the electro-migration effect to selectively open up metal connections (e.g., fuses) at desired locations within an integrated circuit.
However, prior art e-fuse devices using electrically parallel layers of silicon and poly-silicon, as well as W-contact structures, are not as desirable because they require high temperature and high power, which causes damage to neighboring elements.
Therefore, there is a need in the art for an e-fuse device featuring a low voltage, low temperature programming process that is less destructive to neighboring devices.